(a) Field of the Invention
The present invention relates to a super absorbent polymer and a preparation method thereof.
(b) Description of the Related Art
A super absorbent polymer (SAP) is a synthetic polymeric material capable of absorbing water five hundred up to one thousand times the mass of its own. The SAP is called by different names according to the developers, for example, a super absorbency material (SAM), an absorbent gel material (AGM), and the like. Commercial productions of the SAP began for use in feminine hygiene napkins, nowadays, the use of SAP may be found in a very wide range of applications, including water combination soils for gardening, water-stop materials for engineering and construction, sheets for raising seeding, freshness-keeping agents in the food distribution field, and materials for sweating rooms, as well as personal hygiene products, such as disposable baby diapers.
Known preparation methods for SAP include an inverse suspension polymerization method or an aqueous solution polymerization method. The method using inverse suspension polymerization is disclosed in, for example, JP S-56-161408, JP S-57-158209 and JP S-57-198714. The method using aqueous solution polymerization includes several methods: a thermal polymerization method including polymerization of a hydrogel polymer by shearing and freezing in a kneading machine provided with several spindles, and a photopolymerization method using UV radiations on a high-concentration aqueous solution on a conveyer belt to perform both polymerization and drying at once.
Meanwhile, a water-soluble component, that is, a polymer which is not cross-linked in the preparation method of the super absorbent polymer, is produced. When the water-soluble component has a high content, a solution absorption capacity of the super absorbent polymer is improved; meanwhile, when the super absorbent polymer contacts a liquid, the super absorbent polymer is easily eluted to make a surface sticky or to have a negative effect on a skin to be contacted. In addition, when the water-soluble component has a high content, the eluted water-soluble component generally remains on the surface of the super absorbent polymer to make the super absorbent polymer sticky, such that permeability which is a capacity of rapidly delivering a solution to other super absorbent polymers is decreased.
Therefore, development of a super absorbent polymer having high absorbency and excellent permeability has been demanded.